1. Field of the Invention
This invention relates to a proximity switch, and more particularly to a proximity switch having a means for detecting mutual interference when it is arranged in parallel with another proximity switch.
2. Discussion of the Related Art
A conventional high frequency type proximity switch is designed to oscillate at a predetermined high frequency by its oscillator and to decrease its oscillation level when a metal object approaches the proximity switch, whereby an object is detected in response to a change of the oscillation level. When a plurality of such conventional switches are disposed in a parallel relationship, however, a beat phenomenon occurs when the magnetic fields generated by the oscillation coils cross each other so that the proximity switches erroneously detect objects or chattering cause on reversal of signals.
Accordingly, it may be proposed that the respective oscillation frequencies of the proximity switches are designed to be different in order to avoid such mutual interference. There has been proposed a different frequency type proximity switch having a different oscillation frequency to reduce a mutual interference distance. The proposed proximity switch, however, has the disadvantages that a plurality of the proximity switches cannot be closely arranged due to its uneven frequency and reliability against mutual interference cannot be assured when it is mounted within a predetermined distance.